Niobium microalloying of heavy plate pre hardened tool & machine tool

The last few decades have seen rapid development of hard machining steels having higher hardness, approximately >380 HBW, which itself has enabled the development of tool and machine/engineering steels being delivered as pre-hardened (quenched and tempered) from the steel producer. When compared with conventional tool/machine steels, such steels demonstrate numerous advantages, among which the most important are: (i) shorter manufacturing time due to elimination of any heat treatment stage; (ii) guaranteed mechanical properties, and; (iii) a shorter time to market for new products. This paper focuses on the development and introduces the market of two grades, having nominal hardness of 300 and 450 HBW respectively, with low alloy contents giving them much better machinability when compared with traditional tool steels of similar hardness. The paper discusses the additional improvements gained in toughness, in combination with reduction and elimination of expensive alloys via a combination of niobium/titanium microalloying pertaining to effectively control the austenite grain size in the production route. Furthermore, the redesigned steels have been found to be more versatile in being suitable for moulding, cold-work as well as for hot-work applications. Their low alloy content also makes these new steels attractive in substituting commonly used machine/engineering steel grades. (AU) © TMS